The present invention relates to a method for cremating human or animal bodies in a combustion chamber, method whereby the interior atmosphere of the chamber is taken to very high temperature then the body to be incinerated, in its coffin, is introduced, the interior temperature of the chamber being sufficiently high to provoke combustion of the coffin and the body and air is injected into the chamber to supply combustion with oxygen. It also relates to a cremation furnace comprising a combustion chamber, preferably a post-combustion chamber, means for taking the interior atmosphere of the or said chambers to very high temperature and air injection means.
The temperature to which the atmosphere inside the combustion chamber is to be taken is of the order of 800xc2x0 C. This temperature is obtained by any appropriate means, burner or heating element. In order to obtain cremation of the body, it is necessary to supply the combustion chamber with oxygen; this is effected by injection of air all along the cremation. This supply of outside air, which is cold, relatively to the temperature of the chamber, necessitates maintaining the heating means in action.
The gaseous rejects from a cremation furnace are subjected to severe standards. This is why cremation furnaces comprise a post-combustion chamber whose temperature is generally high, of the order of 850xc2x0 C. The standards impose a minimum retention time, i.e. a minimum time during which a certain gaseous volume must dwell in the post-combustion chamber at the temperature in question. This retention time has been determined so as to avoid any detrimental gaseous rejection into the atmosphere, particularly of dioxin.
The purpose that Applicants have set is to propose a method of cremation which makes it possible to optimalize the consumption of energy of the furnace while respecting the quality of the gaseous rejections.
This purpose is perfectly attained by the method of cremation of the invention wherein, in characteristic manner, a turbulence is created from a wall of the combustion chamber, in the form of a swirling displacement above the body and the air required for combustion is injected into this turbulence.
An intimate mixture of the fuels, close to the stoichiometric ratio, may thus be made in the interior volume of the chamber. The turbulence is preferably generated by a rotating means directed inside the chamber and equipped with an air inlet duct, provided with a closing valve and the air injection is adjusted by actuating the valve. According to this particular arrangement, the air is sucked from the duct due to the depression created by the rotating means and moves inside the chamber at the same time as the turbulence generated by said means.
The method of the invention advantageously comprises, on the one hand, a step of pre-heating of the combustion chamber during which the rotating means rotates at reduced speed, for example 25 Hz, and the air inlet valve is closed and, on the other hand, a step of cremation proper during which the rotating means rotates at high speed, for example 40 Hz, and the valve is open. The turbulence, of lesser importance, generated during the operation of pre-heating, without injection of air, makes it possible to homogenize the temperature inside the chamber.
Opening of the valve is preferably adjusted in order to maintain the rate of oxygen of the gases evacuated from the furnace to a minimum threshold, for example of the order of 6 or 7%. This rate corresponds to the standards in force. Applicants have ascertained that, when the cremation furnace also comprises a post-combustion chamber, thanks to the method of the invention, it was possible to obtain the regulatory conditions of gaseous rejects for a retention time clearly less than the threshold imposed.
It is another object of the invention to propose a cremation furnace especially designed for carrying out the method mentioned above, this furnace comprising in known manner a combustion chamber, means for taking the interior atmosphere of the chamber to high temperature and means for injecting air. In characteristic manner, the furnace of the invention also comprises a rotating means which is built in a wall of the combustion chamber, above the location of the body, directed towards the interior of said chamber, being adapted to generate a swirling displacement of the atmosphere; this rotating means is equipped with an air inlet duct on which an adjustable closing valve is placed.
According to a preferred version, the interior volume of the combustion chamber is cylindrical, with a door disposed in one of the two circular transverse walls and the rotating means is placed in the transverse wall opposite the door. The interior cylindrical shape is combined with the swirling displacement in order to ensure the desired homogeneous mixture.
Being question of a cremation furnace whose combustion chamber comprises a sole piece, intended to receive the body, which lines the lower part of said chamber, the sole piece characteristically presents a continuous inner cavity opening out laterally towards the interior volume of the chamber. In this way, during the swirling displacement, the hot atmosphere which is found in the chamber also circulates in the continuous interior cavity of the sole piece so that the latter remains constantly at the temperature of the chamber.
The rotating means advantageously comprises plane, radial blades, mounted on a rotating shaft and disposed axially in a substantially cylindrical housing; moreover, a circular protection screen partially and centrally obturates the circular face of the housing which is turned towards the inside of the chamber; finally, the rotating means also comprises a means for driving the shaft at variable speed.
The circular screen performs a double role. On the one hand, it ensures thermal protection of the blades and, on the other hand, it generates the swirling displacement from an annular zone.
In a preferred embodiment in which the cremation furnace comprises a principal combustion chamber and a post-combustion chamber connected to the principal chamber by a ferrule equipped with a chimney stack for evacuation of the gaseous rejects, each chamber is provided, in characteristic manner, with a rotating assembly mentioned above with variable speed drive, an oxygen sensor is disposed in the chimney stack for evacuation of the gaseous rejects, a heat probe makes it possible to measure the temperature of the combustion chamber and the cremation furnace comprises an electronic control circuit, with clock, said circuit being connected to the oxygen sensor, to the heat probe, to the variable speed drives of the two rotating means and to the closure valves of the two air inlet ducts, said electronic circuit being programmed so as to carry out the following steps:
a) a step of pre-heating which lasts as long as the temperature measured by the heat probe has not reached a determined threshold, of the order of 800xc2x0 C. for the combustion chamber and 850xc2x0 C. for the post-combustion chamber and during which the variable speed drive of the first rotating means of the principal chamber rotates at low speed, of the order of 25 Hz, the valve being in position of closure,
b) a step of cremation proper during which the first motor of the rotating element of the principal chamber passes progressively from the low speed to a higher speed then remains stationary at said high speed, of the order of 40 Hz, the second motor of the rotating element of the post-combustion chamber being actuated to rotate at low speed, of the order of 25 Hz and the valves being open so that the rate of oxygen measured by the sensor remains less than a determined threshold, of the order of 7%.